Optical communications networks, at one time, were generally “point to point” type networks including a transmitter and a receiver connected by an optical fiber. Such networks are relatively easy to construct but deploy many fibers to connect multiple users. As the number of subscribers connected to the network increases and the fiber count increases rapidly, deploying and managing many fibers becomes complex and expensive.
A passive optical network (PON) addresses this problem by using a single “trunk” fiber from a transmitting end of the network, such as an optical line terminal (OLT), to a remote branching point, which may be up to 20 km or more. One challenge in developing such a PON is utilizing the capacity in the trunk fiber efficiently in order to transmit the maximum possible amount of information on the trunk fiber. Fiber optic communications networks may increase the amount of information carried on a single optical fiber by multiplexing different optical signals on different wavelengths using wavelength division multiplexing (WDM). In a WDM-PON, for example, the single trunk fiber carries optical signals at multiple channel wavelengths to and from the optical branching point and the branching point provides a simple routing function by directing signals of different wavelengths to and from individual subscribers. In this case, each subscriber may be assigned one or more of the channel wavelengths on which to send and/or receive data.
To transmit and receive optical signals over multiple channel wavelengths, the OLT in a WDM-PON may include a multi-channel transmitter optical subassembly (TOSA) and a multi-channel receiver optical subassembly (ROSA). One example of a TOSA includes an array of lasers optically coupled to an arrayed waveguide grating (AWG) to combine multiple optical signals at multiple channel wavelengths. The desired accuracy or precision of the wavelengths in a WDM-PON often depends on the number and spacing of the channel wavelengths and may be controlled in the TOSA by controlling temperature. OLT transceiver modules often are designed to fit a relatively small form factor. One challenge with such OLT transceiver modules is providing temperature control of the laser array and AWG in a relatively small space and with relatively low power consumption.
Another challenge is preventing external heat from adversely affecting the laser wavelengths. The lasers and other optoelectronic components in a multi-channel TOSA are often connected to circuitry by wire bonding. With multiple lasers in a multi-channel TOSA, hundreds of wire bonding connections may be used and linked to the environment external to the TOSA. External heat may thus be conducted to the lasers via the wire bonding and may affect the wavelengths of the lasers.